Carbon fiber reinforced polymer composites have been extensively used in different applications owing to their high specific strength and stiffness, excellent corrosion resistance. The composites made of polymeric resin reinforced with continuous or discontinuous fibers, whiskers, particles and now nanomaterials. The composites material made from constituents that remain recognizable individually in the composite. In the late 1950s, fiber composite materials were known to many engineers and their advantages in the term of corrosion resistance, light weight and high strength were apparent. The fiber is the load bearing component and the matrix dissipates loads to the fibers, maintains fiber orientation and protect fibers from extreme environmental conditions. The composites are classified according to their matrix phase such as polymer matrix composite, metal matrix composites and ceramic matrix composites. Glass-reinforced polymer matrix (plastic) composite was commonly used because of specific mechanical properties (strength per unit weight) superior than steel and aluminum. Since after the carbon fiber known, which has high specific strength as compared to glass fibers, lots of work is in progress for its use in different applications. The strength and stiffness of carbon fibers are provided of course, in just one direction in space-along the axis of the fiber and well aligned in unidirectional orientation and should have high reinforcement volume fraction.
In general, the composites are fabricated through impregnation of fibers (with high strength and high modulus) into resin matrices. In practice prepregs consisting of unidirectional or woven fiber fabrics are usually prepared prior to fabrication of the composites [E. Bkyarova, E. T. Thostenson, A, Yu, H. Kim, J. Gao, J. Tang, et al, Multiscale carbon nanotubes-carbon fiber reinforced for advanced epoxy composites, Langmuir 2007, 23, 3970-4]. In unidirectional polymer matrix composites strength is dominated by fiber volume contents [Effect of fiber volume fraction on mechanical properties of carbon fiber composites, [S. R. Dhakate, R. B. Mathur and T. L. Dhami, Mechanical properties of unidirectional carbon-carbon composites as function of fiber volume contents, Carbon Science 3, 3, 1-6, 2002]. While the laminated composites made from prepreg, the fiber fabric dominate the in-plane mechanical properties that are typically high enough for applications, whereas resin matrix dominates out of plane properties that are significantly lower than the in plane properties [J. Zhu, A. Imam, R. Crane, Processing a glass fiber reinforced vinyl ester composite with nanotubes enhancement of interlaminar shear strength, Composite Sci Technol. 2007; 67:1509-17] due to the poor bulk matrix and fiber-matrix interfacial properties. In order for carbon fiber reinforced polymer composites to offer better design choice over typical metallic structure for high end applications such as aerospace and military structures, significant improvements in their out of plane (Z-direction) properties are necessary. It is well known that composite structures in the form of laminates are extremely susceptible to cracks initiation and propagation along the laminar interfaces in various failure modes. The delamination is one of the most prevalent life limiting crack growth modes in laminate composites as delamination may cause severe reductions in in-plane strength and stiffness, potentially leading to catastrophic failure of the whole structure [J. K. Kim, Y. W. Mai, Engineered interfaces in fiber reinforced composites, Oxford Elsevier, 1998; J. K. Kim, Y. W. Mai, high strength, high fracture toughness fiber composites with interface control-a-review. Composite Sci. Technology, 1991, 41, 333-78]. In this direction several techniques has been devised to improve the delamination resistance [K. Dransfield, C, Baillie, Y. W. Mai, Improving the delamination resistance of CFRP by stitching—a review, Composite Sci. Technol. 1994, 50, 305-17; J. K. Kim, Methods for improving impact damage resistance of CFRPs. Key Eng. Mater. 1998; 141(143) 149-68, A. P. Mourutz, Review of Z-pinned composite lamintes, Compos, A. 2007; 38: 2383-97; M. Hoja, S. Matsuda, M. Tanaka, S. Ochiai, A. Murakami, Mode I delamination fatigue properties of interlayer-toughened CF/epoxy laminates. Compo Sci. Technol, 2006; 66: 665-75] such as designing 3D fabric architecture, transverse stitching or pinning the fabrics, fiber hybridization, toughening the matrix resin, and placing interleaves made of tough resin materials in the interplay regions of the laminates. These methods improved the inter-laminar properties but at the cost of the in-plane mechanical properties [C. A, Steeves, N. A. Fleck, In-plane properties of composite laminates with through-thickness pin reinforcement. Int. I. Solids Structures 2006; 43: 3197]. Therefore, it is necessary to find the effective technique to improve the toughness-thickness properties without compromising other mechanical and fracture properties of the composites.
With recent development of nanomaterials/nanotechnology since after discovery of carbon nanotubes by Ijima, polymer composites reinforced with nanoscale fillers have attracted growing interests among scientific community. The polymer composites reinforced with nanotubes, nanofibers and nanoparticles in matrices are expected to possess superior mechanical properties. However, several technological issues such as inadequate dispersion, alignment, and low volume fraction of nano-reinforcement, poor interfacial bonding strength and load transfer etc., the improvement of mechanical properties achieved so far are considerably lower than what have been predicated, in particular when compared to advanced composite reinforced with high performance continuous carbon fibers [Alexandre M, Dubois P. Polymer-layered silicate nanocomposites: preparation, properties and uses of a new class of materials. Mater SciEng R 2000; 28:1-63. Thostenson E T, Ren Z F, Chou T W. Advances in the science and technology of carbon nanotubes and their composites: a review. Compos SciTechnol 2001; 61:1899-912. Njuguna J, Pielichowski K. Polymer nanocomposites for aerospaceapplications: properties. AdvFunct Mater 2003; 5:769-78. Thostenson E T, Li C Y, Chou T W. Nanocomposites in context. Compos SciTechnol 2005; 65:491-516. Coleman J N, Khan U, Gunoko Y K. Mechanical reinforcement of polymers using carbon nanotubes. Adv Mater 2006; 18:689-706. Tjoing S C. Structural and mechanical properties of polymer nanocomposites. Mater SciEng R 2006; 53:73-197. Chou T W, Gao L M, Thostenson E T, Zhang Z G, Byun J H. An assessment of the science and technology of carbon nanotube-based fibers and composites. ComposSciTechnol 2010; 70:1-19]. It is reported that nanoscale reinforcements could distinguishably enhance the toughness and damage tolerance of traditional structural composites used broadly in aerospace structures [Bkyarova E, Thostenson E T, Yu A, Kim H, Gao J, Tang J, et al. Multiscale carbon nanotubes-carbon fiber reinforcement for advanced epoxy composites. Langmuir 2007; 23:3970-4. Thostenson E T, Gangloff J J, Li C Y, Byun J H. Electrical anisotropy in multi-scale nanotubes/fiber composites. ApplPhysLett 2009; 97:073111. Dzenis Y A, Reneker D H. Delamination resistant composites prepared by small diameter fiber reinforcement at ply interfaces. U.S. Pat. No. 6,265,333; 2001. Dzenis Y. Structural nanocomposites. Science 2008; 319:419-20. Wu X F. Fracture of advanced polymer composites with nanostructured interfaces: fabrication, characterization and modeling. Germany: VDM Verlag Publishing House; 2009]. It is predicted theoretically and validated by some experiments that the hybrid multi-scale fiber-reinforced composites with uniformly distributed nano-reinforcement filler (between neighboring composite laminas/prepregs) would possess much enhanced mechanical properties [Dzenis Y A, Reneker D H. Delamination resistant composites prepared by small diameter fiber reinforcement at ply interfaces. U.S. Pat. No. 6,265,333; 2001. Dzenis Y. Structural nanocomposites. Science 2008; 319:419-20. Wu X F. Fracture of advanced polymer composites with nanostructured interfaces: fabrication, characterization and modeling. Germany: VDM Verlag Publishing House; 2009]. So, one promising approach is based upon incorporation of nano-reinforcement agents/fillers between composite laminas/prepregs to form hybrid multi-scale composites. But still the mechanical properties of many hybrid multi-scale composites that have been developed so far are not as high as expected due to the technological challenge on uniform dispersion of nanoscale fillers in highly viscous resins. Hence, it is important to develop a process to fabricate laminated polymer composites with uniformly dispersed nano-reinforcements in the interlaminar regions. So that properties of carbon fiber is exploited in the larger extent in the carbon fiber reinforced polymer composite.
With the discovery of nanotubes by Japanese scientist Ijima, polymer composites reinforced with nanoscale fillers/agents have attracted growing interests among researchers. The polymer composites reinforced with nanotubes, nanofibers, and/or nanoparticles in matrices are expected to possess superior mechanical properties. However, due to several technological issues e.g., poor dispersion/alignment and low volume fraction of nano-reinforcements, poor interfacial bonding strength and load transfer, etc., mechanical properties achieved so far are considerably lower than what is predicted, in particular when compared to advanced composites reinforced with high-performance continuous fibers [M. Alexandre, P. Dubois, polymer-layered silicate nanocomposites: preparation, properties and uses of new class of materials. Mater SciEng R 2000, 28, 1-63; E. T. Thostenson, Z. F. Ren, T. W. Chou, Advances in the science and technology of carbon nanotubes and their composites: a review, Composites Science and technology 2001, 61, 1899-912; J. Njuguna, K. Pielichowski, Polymer nanocomposites for aerospace applications: properties. AdvFunct Mater 2003, 5, 769-78; E. T. Thostenson. C. Y. Li, T. W. Chou, Nanocomposites in content Composite Science and technology 2005, 65, 491-516; J. N. Coleman, U. Khan, Y. K. Gun'ko, Mechanical reinforcement of polymers using carbon nanotubes. Adv Mater 2006, 18, 689-706; S. C. Tjoing, Structural and mechanical properties of polymer nanocomposites, Mat SciEng R 2006, 53, 73-197; T. W. Chou, L. M. Gao, E. T. Thostenson, Z. G. Zhang, J. H. Byun, An assessment of the science and technology of carbon nanotubes based fiber and composites, Composite Science Technology 2010, 70, 1-19].
One of the problem of the carbon fiber laminate reinforced polymer composites is due to ply-by-ply nature of resin composites, susceptibility to delamination along interlaminar planes is an intrinsic and severe problem in the 2D polymer composite [A. C. Carg, “Delamination—A Damage Mode in Composite Structures,” Engineering Fracture Mechanics, 1986, 29, 557-584]. The delamination substantially reduces load carrying capacity and durability of composites and has led disastrous structural failure. In this direction to various effort has been undertaken to improve delamination resistance. Resin chemistry has been modified by incorporating the nanomaterials to improve fracture toughness of resin. It is presume that due to extra ordinary high properties of nanomaterial it has been expected that nanocomposites not only control the delamination but also helped in improving properties of polymer based composites. However recent investigations have revealed that nanoscale reinforcements could distinguishably enhance the toughness and damage tolerance of traditional structural composites used broadly in aerospace structures [X. F. Wu, Fracture of advanced polymer composites with nanofiber reinforced interface, PhD Thesis, University of Nebraska-Lincoin, 2003; P, Karapapas, S. Tsantzalis, E. Flamegou, A. Vavouliotis, K. Dassios, V. Kostopoulos, Multiwalled carbon nanotubes chemically grafted and physically adopted on reinforcing carbon fibers. Adv Composites letter 2008, 17, 103-7]. One promising approach is based upon incorporation of continuous nano-reinforcement agents/fillers between composite laminas/prepregs to form hybrid multi-scale composites. In this direction some studies has been carried out so for.
Y. A. Dzenis et al, incorporated the nanofibers interface in fiber reinforced polymer composites. [Y. Dzenis, Structural nanocomposites. Science 2008; 319:419-20] In advanced aerospace based carbon fiber-epoxy composites less than 1 wt. % of polymer nanofibers improved static and fatigue peel and shear interlaminar fracture toughness [Y. A. Dzenis, Darrll H, Renkar, Delamination resistant composites propertied by small diameter fibers reinforced at ply interface, U.S. Pat. No. 6,265,333, 2001].
S. U. Khan et al, introduced carbon nanofiberbucky paperin between the unidirectional carbon fiber prepreg. The interlaminar shear strength and fracture toughness of multiscale composites containing bucky paper increases by 31% and 104% as compared to composite without bucky paper at interface [S. U. Khan, J. K. Kim, Improved interlaminar shear properties of multiscale carbon fiber composites with bucky paper interleave made from carbon nanofibers, carbon 50, 2012, 5265-5277).
Q. Chen et al, used electrospun carbon nanofibers sheet to sandwich between carbon fiber fabric to develop hybrid multiscale epoxy composites. One sheets carbon nanofiber put between the two carbon fiber fabric sheets to prepare the composites. It is reported that, interlaminar shear strength increases by 86% and bending strength 11% as compared to control composite with carbon nanofibers [Qi. Chen, L. Zhang, A. Rahman, Z. Zhou, X. F. Wu, H. Fong, Hybrid multi-scale epoxy composite made of conventional carbon fiber fabric with interlaminar regions containing electrospun carbon nanofibers mats. Composites Part A 42, 2011, 2036-2042). In another course of investigation, Q. Chen et al, PAN based nanofiber directly electrospun on to the conventional T-300 carbon fiber fabric for different time intervals (5, 10, 20 and 30 min). The stabilization and carbonization of PAN based nanofibers on carbon fiber fabric was carried out. The hybrid multiscale epoxy reinforced with electrospun carbon nanofiber-carbon fiber fabric was developed by vacuum resin transfer molding technique. It is reported that flexural strength of hybrid composites increases from 376 MPa to 465 MPa and interlaminar shear strength 27.5 MPa to 88 MPa while modulus from 12.1 to 24.8 GPa for the optimum collection time of PAN nanofiber on the Carbon fiber fabrics 10 min. [Qi Chen, Yong Zhao, Zhengping Zhou, Arifur Rahman, Xiang-Fa Wu, Weidong Wu, Tao Xu, Hao Fong, Fabrication and mechanical properties of hybrid multi-scale epoxy composites reinforced with conventional carbon, Composites: Part B 44 (2013) 1-7]. Recently, electrospun carbon nanofibers are used to modify the epoxy resin to use as matrix for the development of hybrid multi-scale composites by vacuum assisted resin transfer molding. It is reported that addition of 0.3% of carbon nanofibers in epoxy resin is able to increase the impact absorption energy by 79.1%, interlaminar shear strength by 42.2% and flexural strength by 13.6% [Qi Chen, Weidong Wu, Yong Zhao, Min Xi, Tao Xu, Hao Fong, Nano-epoxy resins containing electrospun carbon nanofibers and the resulting hybrid multi-scale composites, Composites par B, 58, 2014, 43-53]. While in the present invention different approach was adapted to improve the strength of carbon fiber fabric reinforced epoxy matrix composites.